بسم الله الرحمن الرحيم
If an expert and reliable Muslim doctor prohibits a sick person from using water and by using water there is a fear of the sickness increasing or a delay in recovery, then in this case the sick person will have the leeway of doing tayammum.
أفضل التطبيق العصري على مسائل القدوري
للمفتي محمد أشرف الاشاعتي
Vol.1 Pg.169